My DVD-RW Drive Wont Recognise DVDs

Hello,

My 'DVD-RW Drive' will not recognise my DVDs the little light flashes (under the place where i put my DVD in) a few times and then goes out and nothing comes up in 'My Computer', the CDs i put in work fine its only DVDs so i can't watch any movies on my computer.
I have a Windows XP Computer (DIMENSION 5150)

It would be super if someone could help me out...